N-alkoxyamines derivatives of sterically hindered amines are prepared generally from the corresponding amines or the N-oxyl derivatives using a hydroperoxide in the presence of a small amount of a metal ion catalyst in a hydrocarbon organic solvent as described in U.S. Pat. No. 4,921,962.
An alkyl borane is generally prepared by the hydroboration of an alkene with borane as described by H. C. Brown, J. Am. Chem. Soc., 82,1960, p4708-4712; J. Org. Chem., 22, 1957, p1136; Organic Synthesis via boranes, Wiley and Sons, NY, 1975, p 17-18. In addition, Brown also described the coupling (yield <70%) of a hydroborated alkene in situ by stoichiometric amount of silver nitrate in the presence of alkali, J. Am. Chem. Soc., 83, 1962, p1001; J. Am. Chem. Soc., 83,1962, p1002. Brown proposed that the aforementioned reaction is the coupling of alkyl radicals generated by a silver alkyl. The kinetics of the decomposition of the silver alkyls is also studied by C. E. H. Bawn, J. Chem Soc., 1960, 3923; Further evidence is observed by G. M. Whitesides where n-alkyl(tri-n-butylphosphine)silver (I) can be thermally decomposed to give alkyl radicals which is subsequently trapped by stoichiometric 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in moderate to poor yield (65%); J. Am. Chem. Soc, 96,1974, p 2806-2813.
The instant invention provides a novel process for the preparation of sterically hindered alkoxyamines in a non-oxidative reaction medium. This allows a variety of functional groups on the starting N-oxyl derivatives without the need of protection (4-keto or 4-hydroxy-TEMPO give corresponding N-ethoxy product in >95% yield). Furthermore, the instant invention can produce primary alkoxyamine derviatives which is not possible in the sited hydroperoxide process.
The instant invention also provides corresponding products in very high to nearly stoichiometric (>90%) yield at low temperature. Unlike the sited references, the instant process can be operated from stoichiometric to a 1% molar catalytic system along with significant higher yields than sited. In addition, the instant process can be operated in an alcoholic or aqueous medium at ambient temperature which is not operative as described by Whitesides.
The instant invention allows the facile synthesis of N-alkyloxy hindered amines from alkenes which are gases, for example, an N-ethyloxy hindered amine from ethene.